MURRYSVILLE, Pa. — The hallways were buzzing with pupils arriving for classes at Franklin Regional Senior High School when screams, shouts and the thunder of running feet broke the morning routine.

"Run, run! He has a knife!" a teacher yelled Wednesday as a boy charged through the first-floor corridor, slashing and stabbing anyone who got in his way in a melee that unfolded like a scene from a horror film.

He fought off a group of boys who tried to pin him down. By the time he was tackled by a security guard and vice principal, he had wounded at least 19 classmates, including three who underwent surgery for what doctors called deep, life-threatening puncture wounds. Two adults also were injured, including the security guard who helped subdue the assailant.

All of the victims were expected to survive, but school officials, students and parents were left shaken by the latest bloody rampage at what should be a safe haven: a public school.

"This is a very difficult day for this community … but also for the country," said Pennsylvania Gov. Tom Corbett, who called the attack "one horrific five-minute period."

The suspect, 16-year-old sophomore Alex Hribal, was charged as an adult Wednesday night with four counts of attempted homicide, 21 counts of aggravated assault and one count of bringing a weapon onto school property, said his attorney, Patrick Thomassey. Hribal was being held without bail at the county juvenile detention center.

The teen, who was treated for a minor hand wound, appeared in court in shackles and a hospital gown, Thomassey said, adding that Hribal's parents found out about the attack on the news and were "devastated."

As a School Safety Consultant, the quick minded folks on campus that pulled the fire alarm and instructed students and staff to disperse couldn't have been more appropriate. We struggle with making quick decisions during drills and clearly this team made a decision in just that fashion -...

"There was no indication there was any reason for this to occur, no sense of trouble about anything," Thomassey said. "He's a good student; he interacted well with other students.... They didn't see this coming; they're mystified and mortified."

Thomassey declined to talk about a motive or whether Hribal had been bullied. Franklin is the only public high school in this Pittsburgh suburb of about 20,000 people.

Police converged on his family's home in Heritage Estates, a hilly community of spacious homes.

Michelle Kresak, who lives nearby, was stunned by news that the boy she remembered as a "super-nice kid" who came trick-or-treating on Halloween could do such a thing, or that it could happen in their quiet suburb. "Oh my God, he was so normal," she said while out walking her dog.

But she added: "Sometimes you don't know. A lot of kids keep it all inside."

Julia Nitchman, who sat near Hribal in an English class, said he seemed like "a kind of quiet kid" who was into computers. She said he didn't seem to have a large circle of friends: "He's very quiet, not very social. He just kind of laid low."

At first, many pupils thought a fight had broken out when they heard the ruckus at about 7:15 a.m., shortly before classes began.

Then the reality set in.

Mia Meixner saw a classmate who had fallen in the hallway stand up. He lifted his shirt to reveal a stab wound to his stomach.

"I saw blood gushing everywhere," said Meixner, 16. She said the stabber began sprinting down the hallway, knocking people over.

Cameron Lazor, also 16, said she saw the assailant holding two knives — described by police later as measuring 8 to 10 inches long each.

Lazor watched the attacker struggle with some boys trying to subdue him. He escaped after wounding one of the boys and continued his rampage, stabbing anyone who did not run fast enough to escape the flailing blades.

"It was frantic. No one knew where to go," Lazor said.

Students dropped their textbooks and ran, leaving their lockers hanging open.

Trinity McCool, a sophomore, says the attacker came toward her but was stopped by another student, Nate Scimio, who stood between them.

The attacker slashed Scimio, then began chasing McCool and a friend until apparently turning away.

At some point, somebody pulled the fire alarm, alerting pupils throughout the school to head outside.

By then, several of the wounded were lying in the parking lot and on the lawn surrounding the school.

Aubrey Livengood, a sophomore who had been in the library, saw a boy lying on the grass, clutching his side where he'd been stabbed. "A teacher was over him applying pressure and screaming for the nurse," she said.

Police said pulling the fire alarm may have saved lives.

"Under these circumstances … the first thing you want the students to do is to run," said Murrysville Police Chief Thomas Seefeld.

And run they did, pouring out the front doors of the high school as police and ambulances arrived. Recordings of emergency calls revealed a soundtrack of shouts and screaming.

"I don't know what's going down here at school, but I need some units here ASAP," one official radioed.

"Be advised: Inside the school we have multiple stab victims, OK?" another said.

A medical helicopter was dispatched to the scene to carry some of the wounded to hospitals.

Local TV showed video of the boy, his head hanging down, seated in the back of a police car.

By Wednesday evening, officials said two people remained in critical condition.

At a news conference, Seefeld said the rampage lasted about five minutes and occurred in a section of the school that spans a couple hundred feet. The short distance appeared to have allowed the stabber to attack multiple people in a short period of time, Seefeld said.

"The hallways were pretty much in chaos, a lot of evidence of blood on floors and hallways," he said.

Police would not detail the security system in place at the high school, but an employee of a company that provides guards for the campus said it had no metal detector. In an interview with the Pittsburgh CBS affiliate, the employee, Jeff Dahlke, said security officials had visited the campus Tuesday to see about possibly installing metal detectors or finding other ways to make the campus more secure.

Seefeld said the first call for help came in at 7:13 a.m. from William "Buzz" Yakshe, a school resource officer who reported a "critical incident." Police arriving at the scene found one security guard who had been stabbed inside with the handcuffed suspect.

Sam King, a vice principal at the school, had tackled the suspect and held him down with the aid of another school employee, Joan Mellon, enabling Yakshe to handcuff the boy, Seefeld said.

"He's the best man ever," Natalie Tedesco, a senior, said of King, who lives a few doors up from the alleged attacker. Tedesco was visiting some of the wounded at Forbes Regional Hospital, where eight victims were taken and three underwent emergency surgery.

"Today was scary. It was numbing," she said as she left the hospital.

As the city prepared to hold prayer services for the victims, Gov. Corbett, a Republican, said the incident highlighted the need to address mental health and anger issues that he said afflict all levels of society.

A 16-year-old student armed with two knives stabbed and slashed at least 19 classmates and two adults at his high school east of Pittsburgh. The boy was tackled by school employees and taken into custody. All of the wounded are expected to survive.

MURRYSVILLE, Pa. — It took only a few minutes, what the governor would call “one horrific five-minute period,” for a 16-year-old high school student wielding two kitchen-size knives to attack 21 people at Franklin Regional Senior High School outside of Pittsburgh on Wednesday. Hours after the onslaught,...

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